Hollow fiber blood oxygenator

ABSTRACT

A hollow fiber blood oxygenator is provided having a plurality of enclosed, coaxial heat exchanger coils, having a common header to insure uniform temperature in the coils. An enclosed fiber bundle is concentrically positioned inside the heat exchanger coils to define a flow path around the coils and through the fiber bundle. The heat exchanger coils and the outside of the fiber bundle are tapered to provide a close fit. Gas manifolds direct gas flow to and from the hollow fibers.

This application is a divisional of application Ser. No. 07/302,422,filed Jan. 26, 1989, now U.S. Pat. No. 5,124,127.

This invention relates generally to the field of blood oxygenators, andspecifically to hollow fiber blood oxygenators.

BACKGROUND OF THE INVENTION

Blood oxygenator systems are used in open heart surgery and forproviding emergency cardiopulmonary assistance. In both instances, theoxygenator takes over, either partially or completely, the function ofremoving carbon dioxide from the blood, and replacing it with oxygen, asis normally done by the patient's lungs.

A typical use of a blood oxygenator is shown with respect to FIG. 12, inwhich venous blood is removed from a patient and placed in a venousreservoir. A blood pump pumps the blood through an oxygenator whichreplenishes the oxygen in the blood. A heat exchanger adjusts thetemperature of the blood to unduce hypothermia or to maintainnormothermia during surgery. The oxygenated blood then passes through anarterial filter to remove any bubbles, whereupon it is returned to thepatient.

Within the oxygenator itself, the venous blood which is depleted inoxygen and enriched in carbon dioxide, is placed in contact withmicroporous membranes. The membranes have an enriched oxygen gas on oneside, and the depleted oxygen blood on the other side of the membrane.Oxygen passes from the gas, through the membrane, into the blood.Concurrently, carbon dioxide passes from the blood, through themembrane, into the oxygen gas. The oxygenated blood is returned to thepatient.

There are two types of membrane blood oxygenators currently available.The first type is referred to as a flat plate membrane oxygenator, andemploys one or more thin, flat sheets of microporous membrane. Oxygen isplaced on one side of the membrane, and oxygen-depleted blood is placedon the other side of the membrane, with the gas transfer taking placeacross the membrane.

The other type of membrane oxygenator is the hollow fiber oxygenator.This type of oxygenator uses hundreds or thousands of microporous orsemi-permeable hollow fibers to achieve the gas transfer. The hollowfibers are sealed in the end walls of a housing such that a gas can bepassed through the length of the hollow fibers. Blood is passed aroundthe outside of the fibers with the gas transfer occurring across thewalls of the plurality of fibers. In some devices, the blood flowsthrough the hollow fibers with the oxygen gas flowing around the outsideof the fibers to achieve the gas transfer.

The hollow fiber blood oxygenators typically have the fibers packed in acylindrical shaped bundle, with the bundle length and the diametervarying depending upon the amount of gas transfer area desired. Thehousing into which these cylindrical bundles are placed is sized tocorrespond to the bundle diameter and length in order to ensure that allof the blood contacts the fibers, and contacts as many fibers aspossible. Moreover, a close fit between the fiber bundles and thehousing is desirable since it reduces the "priming volume" of fluidneeded to fill the housing and fiber bundle and prevents blood fromshunting around or bypassing the fiber bundle.

It is difficult, however, to maintain an accurate diameter on the fiberbundles because of the small size and flexibility of the individualfibers. For example, the hollow fibers can have an inside diameter ofabout 400 microns with a wall thickness of about 25 microns. Thesefibers are formed into a fiber bundle by winding them onto a core, andduring the winding, the fibers may be pulled and stretched resulting inphysical dimensional variability. The small size of these fibers thusmakes it difficult to maintain accurate dimensions on the diameter ofthe wound fiber bundles which, in turn, increases manufacturing andassembly costs of blood oxygenators having close tolerances on the fitbetween the fiber bundle and the housing. There is thus a need toprovide a more simple and efficient means for insuring a close fitbetween the housing and the fiber bundle in order to provide for a lowpriming volume and prevent blood from bypassing the fibers in the fiberbundle.

A heat exchanger is usually used in conjuction with a blood oxygenatorin order to control the temperature of the blood returned to thepatient. The heat exchange is typically achieved by passing the bloodover a heated surface. There is a need, however, for an efficient,compact heat exchanger having a low priming volume and low flowresistance.

SUMMARY OF THE INVENTION

The present invention provides a combined blood oxygenator and heatexchanger having a compact configuration, low priming volume, and lowpressure drop with high oxygenation and heat exchange efficiencies.Moreover, the unit has several subassemblies which are preferablytapered to not only provide an easier and quicker assembly, but topermit the use of less exacting and expensive manufacturing techniques.

Still further, while there are a plurality of individual heat exchangingcoils used in the heat exchanger, the temperature in each of the coilsis uniform because the heating fluid is provided from a common header ormanifold which eliminates hot spots and cold spots in the individualcoils.

Still further, a fluid port allowing sampling of the oxygenated blood isprovided at the top of the oxygenator, where it is readily accessible.This is a great improvement over the prior versions which requiredaccessing a port on the bottom of the oxygenator with extendedcontortions and bending to reach the port.

Finally, a means for removably attaching a venous reservoir to the bloodoxygenator unit itself is provided. This detachable reservoir allows theuse of fewer components during an operation, and allows a common venousreservoir to be used during surgery as well as being used forpost-surgery drainage of the wound.

The hollow fiber oxygenator of this invention uses semi-permeablemicroporous fibers which are wound about a tapered hollow core with thelength of the fibers being enclosed within a flow path of theextracorporeal blood. The fibers are wound onto the tapered core, theends of the core are sealed in potting compound, and after curing theends are cut perpendicularly in order to expose the ends of each fiber.The respective ends of the fibers are enclosed within a gas manifold forthe inlet and outlet of the blood gasses.

The tapered circular periphery of the fibers is enclosed in acorrespondingly tapered interior housing, with the tapers insuring aclose fit between the housing and fiber bundle. There are apertures atthe larger end, or top of the interior housing, and at the small end ofthe tapered core to allow the passage of extracorporeal blood along thelength of the fibers.

An integral heat exchanger comprises an anodized aluminum heat exchangerwith a plurality of circular, coaxially arranged coils in which eachcoil circles one and a half times (about 540°) before diverging to aheader. Advantageously, the plurality of coaxial coils are arranged in atapered configuration to correspond to the taper of the fiber bundlesencased in the interior housing. An outer casing or housing surroundsthe heat exchanger coils and includes longitudinally arranged headerssurrounding the ends of the coils so that water flowing into an inletheader circulates through each of the individual coils around theinternal periphery of the housing, and exits at an outlet header. Theplurality of coils are inserted as a unit into the outer casing, andthen potted in position to provide a sealed heat exchanger unit enclosedin the outer housing.

The encased fiber bundle is inserted inside of the heat exchanger coilsin the outer casing, with the interior housing cooperating with theouter casing to enclose the heat exchanger coils in an enclosed annularspace defining a fluid flow path through the heat exchanger. Theinterior housing is sealed to the outer casing at the top and bottomends in order to define appropriate flow paths through the heatexchanger and fiber bundle. Top and bottom caps are then applied todefine appropriate gas manifolds or gas flow paths communicating withthe inside of the hollow fibers in the fiber bundle.

In operation, water passes through the heat exchanger to adjust thetemperature on the coils. Blood is introduced through the bottom of theouter casing at the bottom of the heat exchanger and flows upwardly overa plurality of the heat exchanger coils, into the apertures at thelarger end, or top of the interior housing, and then downwardly over thehollow fibers for the transfer of blood gasses. The oxygenated bloodthen passes through the openings at the bottom or small end of thecentral core and out a bottom arterial blood outlet. Oxygen gas ispassed through the top cap and gas manifold, through the hollow fibersto oxygenate the blood and remove carbon dioxide, and then out thebottom cap and gas manifold.

In one embodiment of this invention, the oxygenator contains an enclosedfiber bundle unit comprising a bundle of hollow fibers open on theirends for ducting gas therethrough with a casing around the fiber bundle.The casing is tapered at a predetermined angle. A fluid inlet and afluid outlet are provided on the casing for ducting fluid around theoutside of the fibers.

The oxygenator also contains a heat exchanger unit comprising a stack oftubular, coaxial coils defining an inner cavity tapered at thepredetermined angle and corresponding in size to the exterior of thecasing. The bundle unit is concentrically positioned within this cavityand compressed against the coils. The bundle unit cooperates with theheat exchanger unit to define a fluid flow path around the outside ofthe coils. The heat exchanger unit also has fluid inlet and a fluidoutlet for ducting fluid through the inside of the coils.

The oxygenator further contains cap means cooperating with the heatexchanger unit to define gas passages which provide gas to the hollowfibers and remove gas from the fibers. The predetermined taper angle isadvantageously about 2°, but may be up to about 6°.

In further variations, the oxygenator has a seal on one end of saidfiber bundle unit for sealing against the heat exchanger unit, and aresiliently mounted seal on the opposite end of the fiber bundle unit toseal against the heat exchanger unit and to facilitate concentricpositioning of the fiber bundle unit and the heat exchanger unit.

Another way of viewing the oxygenator of this invention, is by theconstruction of the flow paths through the oxygenator. There is one flowpath through the inside of a plurality of fibers in the fiber bundle, asecond liquid flow path around the outside of said fibers and around thecoils of the heat exchanger, and a third flow path through the heatexchanger.

In this flow path embodiment, there is a housing around the bundle offibers, sealed at opposite ends of the housing to define the gas flowpath through the inside of the fibers. There is also a fluid inlet atone end, and a fluid outlet at the other end of the housing for ductingfluid through the inside of the housing around the outside of theindividual fibers to define a portion of a liquid flow path. The heatexchanger unit comprises a stack of tubular, coaxial coils defining aninner cavity corresponding in size to the exterior of the housing. Thebundle unit is concentrically positioned within that cavity andcooperates with the heat exchanger unit to define a portion of theliquid flow path around the outside of the coils. That liquid flow pathfurther communicates with the fluid inlet in the housing. An outercasing enclosing the outside of the stack of coaxial coils also definesthe flow path around the coils.

There is a fluid inlet and a fluid outlet for ducting heat exchangefluid through the inside of the coils to define the heat exchange fluidflow path through the inside of the coils.

The said gas flow path may further comprise a cap cooperating with theheat exchanger unit to define gas passages which provide gas to one endof the fibers and remove gas from the other end of the fibers. When thefiber bundle unit and said the exchanger unit are sealed at oppositeends, the gas cap provides a second, gas-tight barrier which preventsany liquid leaked across the housing seals from entering the gas pathbefore the gas path passes through the fiber bundle.

In a further variation of this embodiment, the outer casing cooperateswith the housing around the fiber bundle to form a cavity above thelocation at which the liquid flow path around the heat exchanger coilscommunicates with the liquid inlet in the housing. This cavity acts tocollect gas escaping from the liquid flow path.

In a further variation of this invention, a fluid reservoir is providedwhich is in fluid communication with the liquid flow path through theoxygenator. Adaptor means on the oxygenator for allow the reservoir tobe removably fastened to the oxygenator.

In a further embodiment of this invention, the fluid outlet on thehousing has a tube communicating with the bottom portion of the bundleof fibers. A plurality of apertures in the tube open to the bundle tofurther define the liquid flow path to the inside of said tube. A bottomcap on the heat exchanger unit encloses the end of the fiber bundle unitthrough which gas exits to define a portion of the gas flow path. Aconduit extending from the bottom cap to one end of the tube furtherdefines a portion of the liquid flow path. The conduit is sealed to thetube to separate the gas path from the liquid flow path.

A sampling liquid flow path may also be added which comprises a passagecommunicating liquid from the inside of the tube to a port on the top ofthe oxygenator. The port is externally accessible to allow sampling ofliquid after the liquid has passed through the fiber bundle.

In a still further embodiment of this invention, the heat exchanger unitused in the illustrated embodiment comprises a plurality of individual,tubular, coaxial coils each of which has an inlet end and an outlet end.The coils are stacked coaxially to define an inner cavity correspondingin size to the exterior of said casing. The fiber bundle unit isconcentrically positioned within this cavity and cooperates with theheat exchanger unit to define a fluid flow path around the outside ofthe coils. A positioning member connects with the ends of the pluralityof coils to maintain the coils in the coaxial stack.

In the illustrated embodiment of the heat exchanger, the coils encirclethe cavity one and one half turns, with the inlet and outlet endsextending tangentially in the same direction from opposite sides of thecoils. A spacer strip connects with a number of the tangential endportions of the coils, with the spacer strip having a plurality ofapertures through which the ends of the coils extend. A spacer assemblyis also provided, which comprises a pair of generally verticallyorientated spacer strips. The spacer strips have a plurality of notchesor apertures with each aperture being sized to receive at least aportion of one of the coils. A plurality of substantially parallelspacer bars connect the spacer members. The spacer bars are curvedaround the periphery of the cavity, positioned between two adjacentcoils, and substantially coaxial with the coils.

The oxygenator of this invention is also constructed such that testingof components is more easily achieved. Thus, another embodiment of thisinvention comprises a bundle of hollow fibers open on their ends forducting gas therethrough. A housing is placed around the bundle, withone end open. A stack of tubular, coaxial heat exchange coils surroundthe housing. A casing encloses the coils, with the casing having an openend surrounding the open end of the housing. The casing and the housingforming an annular passage therebetween. The housing further has aplurality of apertures for fluid communication between the annularpassage and the spaces between the tubes. The ends of the bundle oftubes is sealed between adjacent tubes so that a liquid flow path isformed through the annular passage and through the bundle in the spacesbetween the tubes.

A ring-shaped cover fits onto and is sealed with the casing and thehousing to close the end of said annular passage. A gas cap is placedradially within the cover and encloses the end of the housing. The coverand the cap are separate components so that the flow path may bepressure tested with the cover in place while the cap is not yetinstalled and while the ends of the fibers are accessible for thesealing of leaks in said fibers.

These and other advantages of the invention will be better understoodwith respect to the drawings, a brief description of which is providedas follows, and in which like numbers refer to like parts throughout.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevated perspective view of the oxygenator/heat exchangerof this invention;

FIG. 2 is a lower perspective view at an angle opposite to that used inFIG. 1 of the oxygenator/heat exchanger of this invention;

FIG. 3 is an exploded perspective view of the oxygenator/heat exchangerof this invention;

FIG. 4a is an exploded perspective view of a portion of the heatexchanger assembly of this invention;

FIG. 4b is an exploded perspective view of a portion of the spacerassembly for the heat exchanger coils of this invention;

FIG. 5 is a partially sectioned, perspective view of the oxygenator/heatexchanger of this invention;

FIG. 6 is a partial cross-sectional view taken along 6--6, as shown inFIG. 5;

FIG. 7 is a perspective view of a microporous tubular fiber as used inthis invention;

FIG. 8 is a cross-sectional elevation view of the oxygenator/heatexchanger of this invention;

FIG. 9 is a partially sectioned, exploded perspective view of an encasedfiber bundle as used in this invention;

FIG. 10 is an exploded perspective view of the enclosed heat exchangerunit of this invention;

FIG. 11 is a partially sectioned perspective view of a venous adaptorfor use with this invention; and

FIG. 12 is a schematic depiction of a blood oxygenator and heatexchanger as used during surgery.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIGS. 1 and 5, but primarily to FIG. 5, there is shown theblood oxygenator/heat exchanger 12 of this invention, referred tohereinafter collectively as "oxygenator 12." The basic operation of theoxygenator 12 will be briefly described before explaining the details ofthe construction and operation. A fluid, such as venous blood, which isdepleted in oxygen and rich in carbon dioxide, is introduced to thebottom of the oxygenator 12 at venous inlet port 14. As used herein, the"top" and "bottom" refer to upper and lower portions as viewed in thedrawings.

The blood flows upward under pressure around a plurality of heatexchanger coils 16. At the top of the oxygenator 12 the blood passesthrough a plurality of apertures 18 in interior housing 20. The bloodflows downward under pressure through a fiber bundle 22 during which theblood is re-oxygenated and the carbon dioxide is removed. At the bottom,or small end of the fiber bundle 22, the blood passes through aplurality of apertures 24 in a tapered centered core 26. From there theoxygenated blood exits through a tube 28 which connects the bottom orsmall end of the tapered center core 26 to an arterial port 30.

The oxygen used to replenish the venous blood is introduced into a topcap 32 through a gas inlet port 34. The top cap 32 forms part of a gasmanifold communicating with the top 36 of the fiber bundle 22. Referringto FIG. 5, the gas enters the top 36 of the fiber bundle 22, passesthrough the length of the hollow fibers in the bundle 22, and exits thebottom or small end 38 of the fiber bundles. A bottom cap 40 forms acavity or manifold communicating with the bottom 38 of fiber bundle 22.Gas is allowed to exit through gas vent 42 (FIGS. 1 and 5).

Referring to FIGS. 1 and 5, the temperature is controlled by passing atemperature controlled fluid through the heat exchanger coils 16. Thefluid, preferably water, is introduced through an inlet port 44, whichcommunicates with a manifold or first header 46 which is in fluidcommunication with one end of each of the plurality of heat exchangercoils 16. The fluid passes through the heat exchanger coils 16, andexits at a second header 48 (FIG. 1) which is in fluid communicationwith the remaining ends of the heat exchanger coils 16. A fluid outletport 50 (FIG. 1) allows the fluid to be removed from the header 48.

A plurality of fluid communication ports and a sampling port are alsoprovided in the oxygenator 12 as will be subsequently described.

As illustrated in FIG. 3, the oxygenator 12 is assembled by combiningseveral subassemblies and parts into a completed unit. Brieflydescribed, these subassemblies and parts comprise the top cap 32, anouter casing cap 52, an enclosed fiber bundle unit 54, an enclosed heatexchanger unit 56, and the bottom cap 40. The enclosed fiber bundle unit54 will be described first.

Referring to FIGS. 3 and 5, but primarily to FIG. 5, there is a taperedcentral core 58 having a generally tubular, but tapered, exterior shapesuch that its top end 60 is larger than its bottom end 62. Another wayof describing the tapered central core 58 is that it has afrusto-conical shape. The taper on the central core 58 is about 2°.Adjacent the smaller, or bottom end 62 of the core 58 are located theplurality of apertures 24 which extend through the thickness of the core58. Between the apertures 24 and the larger top end 60, is located aplug 64 which substantially blocks the interior of central core 58. Aplurality of openings or slots 25 (FIG. 5) are located on the exteriorportion of the central core 58 such that they have one end communicatingwith the apertures 24. The slots 25 extend only part way through thewall of the central core 58. A portion of the inside of the core 58,adjacent the smaller or bottom end 62 and apertures 24 is cylindrical inshape.

In the illustrated embodiment, at the center of the plug 64 is located anipple 66 extending towards the larger top end 60 of core 58. A flexibletube 68 is in fluid communication with the nipple 66 that extendstowards the larger top end 60. A one way valve 69 is attached to thetube 68.

A plurality of hollow, microporous fibers are wound onto the uniformlytapered outside of central core 58. A portion of one such hollow tube 70is illustrated larger than actual size in FIG. 7. The tubes 70 comprisemicroporous or semi-permeable membranes in a hollow, tubularconfiguration. A microporous polypropylene hollow fiber membrane, havinga diameter of 400 microns, and a wall thickness of about 25 microns, isbelieved to be suitable for use.

Referring again to FIG. 5, a plurality of the fibers, or tubularmembranes 70 (FIG. 7) are wound onto the central core 58. It is believedsuitable to wind the membranes 70 in bands of 18 fibers with theorientation of the successive layers of the windings being varied. Atotal of abut two square meters of surface area is believed suitable foran oxygenator used with an adult patient. The means of winding suchmembranes 70 onto tubular cores is the subject of a number of patents,and a number of methods are known in the art which could achieve such awinding.

The top and bottom ends 72 and 74 of the fiber bundle 22, as viewed inFIG. 5, respectively, are sealed to provide a gastight seal among theoutside of the plurality of fibers 70 (FIG. 7). Typically a pottingcompound such as urethane is applied to the outside of the fibers andallowed to cure. The bundle of fibers is then cut across the pottingcompound to expose the ends of the plurality of tubes. Thus, gas canflow through the length of the tubes, but cannot flow through the sealedends 72 and 74 of the fiber bundle. To the extent the potting compounddoes not seal the fiber bundle 22 to the ends of the inner core 58, anadditional sealant may be provided to ensure a gastight seal.

The fiber bundle 22 is wound onto the tapered core 58 with asubstantially uniform thickness such that the outer circular peripheryof the bundle 22 has substantially the same amount of taper as thecentral core 58. The central core 58 and fiber bundle 22 are thenenclosed or encased by interior housing 20.

Referring to FIGS. 3 and 5, the interior housing 20 has a frusto-conicalshape, comprising a tubular, tapered housing with a length substantiallyequal to the length of the central core 58. The degree of taper is alsosubstantially the same as the inner core 58. Adjacent the larger, topend of the interior housing 20, as viewed in FIGS. 3 and 5, there arelocated the plurality of apertures 18, which extend through thethickness of the casing 20. The apertures 18 are above a flange or lip76 extending radially outward from the interior housing 20, and a flange78 having a generally "L-shaped" cross-section which extends outward andupward from the interior housing 20.

An O-ring 79 is located in a recess (not shown) on the upward extendingportion of the L-shaped flange 78. The flange 78 thus acts as a springto resiliently urge the O-ring 79 outward against any radiallycompressive force or contacting structure. Adjacent the smaller, orbottom end of the interior housing 20 is another O-ring 77 located in arecess (not shown).

The diameter of interior housing 20 is such that, when it is positionedconcentrically with the central core 58, with the corresponding endsbeing radially aligned, the interior housing 20 is slightly smaller indiameter than the corresponding diameter on the outside of fiber bundle22. The assembly procedure is thus to slide the interior housing 20 overthe core 58 and fiber bundle 22 as far as the interior housing 20 willgo. At that point, the interior housing 20 is pushed further until theends of the casing 20 are positioned radially outward of the ends 60, 62of the central core 58. This final positioning causes some slight radialcompression in the fiber bundle 22, but provides a close fit with thecasing. In the illustrated embodiment, the fiber bundle 22 is woundaround the center core 58, and the casing 20 is positioned before thepotting compound is cut at each end of the enclosed fiber bundle unit54. To ensure a gastight seal, a sealant may be applied between the endsof the interior housing 20 and the mating ends 72, 74 of fiber bundle22.

When the bundle 22 and casing 20 are assembled, the apertures 18 in theinterior housing 20 are located below the potted area at the larger, topend 72 of the bundle 22. Thus, the apertures 18 provide a fluidcommunication means to the fiber bundle 22 which is encased between thecentral core 58 and interior housing 20, and sealed on opposite ends bypotting compound.

The apertures 24 and slots 25 in central core 58 are located above thepotted area on the end 74 of the fiber bundle 22. The slots 25 act toprovide a hole through the tubular wall of core 58 with the size of theopening to the hole being larger on one side of the wall than on theother side. As shown, the wall defining a portion of the fluid flow patharound the outside of the fibers has a plurality of apertures configuredto have a larger opening adjacent the fibers and a smaller opening onthe opposite side of the wall.

The slots 25 effectively increase the contact area or drainage area ofthe apertures 24 with the fiber bundle 22 since blood flows into theslots 25 which in turn channels the blood into the apertures 24. Thus, alarger drainage area and reduced resistance to fluid flow is providedwhile minimizing the size of the apertures 24.

The apertures 24 provide a fluid communication means from the fiberbundle 22 to the inside, bottom (smaller) end of the central core 58.There is thus provided an enclosed fiber bundle having a first flow paththrough the inside of the fibers and a second flow path around theoutside of the fibers.

The fit between the outside of the fiber bundle 22 and the adjacentinterior housing 20 should be as close as possible in order to preventblood from shunting through any gap between the fiber bundle and thehousing. Currently, the outer diameter of cylindrical fiber bundles mustbe closely controlled, and the diameter of the containers into whichthey fit are also closely controlled; even then, a slight gap sometimesoccurs. The use of a tapered core and casing to enclose a tapered fiberbundle allows for a wider variation in the manufacture of the fiberbundle 22 while still insuring a tight fit. There is thus advantageouslyprovided not only a less expensive means of manufacture, but a lessexpensive means of assembly. Moreover, the assembly is less likely todamage the fibers on the outside of the bundle than prior devices andassembly techniques. There is also advantageously provided an enclosedsubassembly of fiber bundles which can be shipped and handled duringassembly with much less chance of damaging the tubular fibers.

The enclosed heat exchanger unit 56 (FIGS. 3 and 10) will be describednext. Referring to FIG. 10, broadly described, the heat exchanger unit56 comprises an outer casing cap 52, an outer casing 92, a plurality ofcoils 16 together with a spacer assembly 84 and spacer strips 85.

Referring to FIGS. 4, 5, 6, 8 and 10, but primarily to FIG. 5, aplurality of individual heat exchange coils 16 are assembled in atapered, coaxial configuration. Preferably, the heat exchanger coils 16comprise anodized aluminum coils. Spiral ribs are formed on the curvedportions of the heat exchanger coils 16 by means known in the art andnot described in detail herein. Each of the coils 16 has an input end 80(FIGS. 4 and 5) and an outlet end 82 for the inlet and outlet of a heatcontrolled fluid, respectively.

The coils 16 are shaped such that they would wrap around afrusto-conical shape having a diameter and taper corresponding to thediameter and taper of the tapered interior housing 20. Thus, the coils16 are wrapped about a circle with the coils 16 adjacent the top orlarger end of the oxygenator (when installed) being wrapped around alarger circle than those at the bottom, narrower end of the oxygenator(when assembled). Alternately phrased, the coils 16 are coaxiallypositioned to define a tapered cavity.

The ends 80, 82 extend at a tangent to the circle and to the coaxialassembly of coils, in the same direction and from opposite sides of thecircle and coaxial assembly of coils. Each of the coils 16 wraps one andone-half times (approximately 540°) about this circular shape.Advantageously, thirteen individual coils 16, each with ends 80, 82, canbe stacked coaxially, positioned by spacer assembly 84 and spacermembers 85. The ends 80, 82 of the stack of coils will form two lines,having a slight "V" shape because of the taper of the stack of coils.

Referring to FIGS. 8 and 10, a pair of spacer strips 85 are shown whichcomprise a longitudinal member having a rectangular cross-section. Aplurality of circular holes are formed in the spacer strips 85 tocorrespond to the size and location of the ends 80, 82 of the coils 16.The ends 80, 82 of the coils 16 are inserted through the holes in thespacer strips 85 with the strips 85 holding the coils 16 in position.The spacer strips 85 have a length approximately equal to thelongitudinal length of headers 46, 48. After the plurality of coils 16are assembled in a coaxial configuration, the assembly is joined to aspacer assembly 84. The spacer assembly 84 as best illustrated in FIG.4a, and comprises two spaced apart longitudinal spacer members 86. Eachof the members 86 have a plurality of cylindrical notches 88 on the sidefacing away from the other member 86. The ends 80, 82 of the coils 16fit into the plurality of notches 88. A plurality of substantiallyparallel, curved spacer bars 90 extend between and join the members 86.The spacer bars 90 occupy substantially the same position as the missinghalf loop on the one and one-half turn coils 16. The spacer bars 90serve to displace volume so the total volume of priming fluid is lower,and also prevent shunting of the fluid which might reduce contact withthe heat exchange coils 16.

The spacer assembly 84 is inserted into the plurality of coaxial coils16 held by the spacer strips 85, with that combined assembly then beinginserted into an outer housing or casing 92, as illustratedschematically in FIG. 10. The outer casing 92 is best described withreference to FIGS. 1 and 5. The outer casing 92 comprises a generallyhollow, frusto-conical shape which has a middle portion 96 which has aninside tapered at an angle corresponding to the taper on the enclosedfiber bundle unit 54 (FIG. 3).

Extending tangentially from opposite sides of the outer casing 92 aretwo longitudinal headers 46, 48 which open into the inside of the outercasing 92. The headers 46, 48 extend for a substantial portion of theaxial length of the outer casing 92 and are shown as extending in thesame direction. The headers 46, 48 form a slight "V" shape because ofthe taper of the outer casing 92 from which they extend. The headers 46,48 are substnatially rectangular in cross-section. Referringadditionally to FIG. 8, the headers 46, 48 contain a space sufficientlylarge to enclose the ends 80, 82 of the plurality of heat exchangercoils 16. An enlarged area 93 extends longitudinally along the length ofheaders 46, 48. The enlarged area 93 comprises a localized increase inthe space between the opposing sides of headers 46, 48, extending thelength of headers 46, 48.

Referring now to FIGS. 1, 2, and 5, there are several stepped changes inthe diameter of the outer casing 92. A bottom portion 94 has thesmallest diameter and extends axially for a distance of about 1.5inches. The bottom portion 94 tapers axially at about 1/2°, with thebottom end being smaller than the top end. The bottom, or free end ofbottom portion 94 terminates in a bottom lip 95 which extends radiallyinward. A plurality of slots 97 are formed in the bottom lip 95 toaccommodate the attachment of bottom cap 40 as described later. Thebottom portion 94 can be made of a uniform diameter, without a taper.

The middle portion 96 has a slightly larger diameter than that of bottomportion 94, and as mentioned above, tapers at an angle corresponding tothat of the encased fiber bundle unit 54. The small end of the middleportion 96 joins the large end of the bottom portion 94. The axiallength of the middle portion 96 corresponds to substantially the axiallength of the plurality of coils 16 on the spacer assembly 84.

A top portion 98, seen best in FIG. 3, has a larger diameter than themiddle portion 96, and is tapered at about 1/2°. The smallest diameterend of the top portion 98 joins the largest diameter end of the middleportion 96.

The headers 46, 48 extend from the upper part of the bottom portion 94,through the middle portion 96, and through the top portion 98. Theheaders 46, 48 are integrally molded with the outer casing 92.

Adjacent the juncture of the bottom portion 94 and the middle portion96, on the side of the casing 92 opposite the headers 46, 48, arelocated two access ports, the venous inlet port 14, and a venoustemperature access port 100 (FIG. 2). These types of ports are known inthe art and are not described in detail herein. As previously mentioned,ports 44, 50 are also formed in the upper portion of the headers 46, 48,respectively (FIG. 1).

Referring to FIGS. 5, 8, and 10, the assembly of the enclosed heatexchanger unit 56 will be described. The combined assembly of the heatexchanger coils 16, spacer strips 85 and spacer member 86 is oriented sothat the ends 80, 82 correspond to the location of headers 46, 48,respectively, and the location of the spacer strips 85 corresponds tothe location of the enlarged areas 93. The assembly of the coils 16, thespacer member 86, and the spacer strips 85 are then inserted withinouter casing 92. The diameter and taper of the middle portion 96 ofouter casing 92 corresponds to the configuration of the assembly ofcoils 16 and spacer members 86 to form a substantially close fit. Thelarger end, or top of the plurality of coils 16 is at or adjacent to thebeginning of the top portion 98 when the coils 16 are placed inside theouter casing 92.

Referring to FIGS. 5 and 6, when assembled, the coaxial coils 16 arelocated between the interior casing 20 and the outer casing 92. The ribson the coils 16 spiral around the coils 16 to create a non-uniformdiameter, which effectively prevents a fluid tight seal from formingwhen the casings 20 and 92 are pressed against the coils 16. Thus, theribs on the coils serve to insure a fluid flow path across the coils 16exists between the casings 20 and 92.

Referring to FIG. 8, the spacer members 86 abut against the outer casing92 when the plurality of coaxial coils 16 are inserted. Preferably, theedges of the spacer members 86 are configured to coincide with theinterior shape of the outer casing 92 so as to form a close fit. Thespacer strips 85 are sized so they abut the inside of the enlarged areas93 in the headers 46, 48.

The enclosed heat exchanger unit 56 is completed by attaching the outercasing cap 52 and sealing the unit to define flow passages for the fluidflow through the heat exchanger coils 16.

Referring to FIGS. 3 and 5, the outer periphery of casing cap 52 isconfigured to correspond to the top of the outer casing 92. The outercasing cap 52 has a generally circular outer shape with two tabs 106extending tangentially, in the same direction, but from opposite sidesof the periphery of cap 52. The tabs 106 are configured to correspond tothe outside peripheral shape of the ends of headers 46, 48 as theyconnect to the outer casing 92. The tabs 106 fit over the headers 46, 48as the cap 52 is placed over the top of the outer casing 92.

The cap 52 has a downwardly depending flange 109 which forms a circularhole or aperture 108 in the center of the cap 52 (FIG. 3). There are aplurality of bayonet apertures 113 (FIG. 3) formed in the flange 109.The flange 109 is substantially cylindrical in shape, having a diameterapproximating that of the L-shaped flange 78 on the interior housing 20.

The outer periphery of the outer casing cap 52 also has a dependingflange 110 (FIG. 5) substantially parallel to the longitudinal axis ofaperture 108. The flange 110 corresponds to the shape of the outerperiphery of cap 52, including the shape of the tabs 106. Spacedslightly inward from the flange 110, is a second locking flange 111(FIG. 5) which depends substantially parallel to, but spaced from flange110. On the side of the cap 52 opposite the tabs 106, is located avenous gas port 112.

Referring to FIG. 5, it can be seen that the flanges 110, 111 arelocated so that the top portion of outer casing 92 fits between theflanges in a sealing manner. Moreover, the tabs 52 fit closely over theoutside of the top of the headers 46, 48. Advantageously, a sealingadhesive can be provided along the periphery of the top portion 98, orbetween the flanges 110, 111, in order to ensure a gastight seal.

After insertion of the cap 52 onto the top of the outer casing 92, apotting material 102 is inserted into the headers 46, 48 so that aportion of the ends 80, 82, spacer strips 85, the spacer members 86 aresealed to the outer casing 92 in a gastight manner. The spacer strips 85are sealed into the enlarged areas 93 by injecting a potting material102, such as a thixotropic urethane, into the enlarged area 93 so thatboth sides of the spacer strips 85 are sealed to the headers 46, 48,while the ends of the coils 80, 82 are left open for the flow of fluidthrough the coils 16. The spacer strips 85 are sized to fight closelywithin the enlarged area 93 so as to provide a semi-seal which helpscontrol the flow of the potting compound 102 around the strips 85. Thespacer strips 85 can be potted in position before the outer casing cap52 is sealed in place.

Spacer assembly 84 is also sealed to the inside of the outer casing 92adjacent the juncture of headers 46, 48 with the outer casing 92. Thespacer assembly 84 is sized to fit close to the corresponding portionsof the inside of casing 92 to provide a semi-seal which helps controlthe flow of potting compound 102. The casing 92 can be positionedhorizontally to help control and direct the flow of the potting compound102. The introduction of the potting material can be achieved throughapertures formed in the casing 92 (not shown), which apertures aresealed by the potting compound 102. The potting material is applied in amanner such that it does not cover the apertures in the ends 80, 82which allow a heat exchanger fluid to pass through the coils 16.

The enclosed heat exchanger unit 56 (FIG. 3) provides a separatelyassembled subassembly which allows movement and handling of a heatexchanger while minimizing damage to the heat exchanger coils. The useof the manifolds or headers 46, 48 allows a fluid of substantiallyuniform temperature to be introduced into the inlet ends 80 of theplurality of coils 16, and allows uniform exit of the fluid from thecoils 16 through the exit header 48. The mixing chamber effect ofheaders 46, 48 prevents any hot spots from occurring throughout anysingle heat exchanger coil 16. The separate assembly of the heatexchanger unit also allows separate testing for leakage of thetemperature control fluid before final assembly of the oxygenator 12.

Referring to FIGS. 1, 3 and 5, the top cap 32 comprises a generallycircular cap having a substantially flat portion with a depending lip114 around its outer periphery. At the upper portion of the top cap 32are located a plurality of bayonet mounting tabs 116 which compriseradially extending projections located at several points around theperiphery of the top cap 32. The spacing of the bayonet mounting tabs116 is such that they correspond with the bayonet slots 113 in the outercasing cap 52. Located on the exterior surface of the top cap 32 is thegas inlet port 34 which communicates with the interior of the top cap32.

Also located on the exterior surface of top cap 32 is an arterial sampleport 118 which communicates with the interior of the top cap 32 and thetube 68 and one way valve 69 (FIG. 5). The sample port 118, via tube 68and nipple 66, allows access to oxygenated blood as it exits the fiberbundle 22 through apertures 24.

Referring to FIGS. 2, 3 and 5, the bottom cap 40 comprises a generallyflat disk having a plurality of L-shaped mounting tabs 119 extendingsubstantially perpendicular to the flat surface of cap 40, with anexterior portion of the tabs 119 extending radially outward thereof. Thetabs 119 are located on the cap 40 to correspond with the location ofslots 97 in bottom lip 95 of the outer casing 92.

At the center of the cap 40 is located the flow tube 28 which comprisesa substantially hollow cylinder extending upward from the bottom cap 40.Adjacent the outermost end of the tube 28 are located two O-rings 120which are seated in a rectangular shaped aperture (not shown) in thetube 28. The diameter of the O-rings 120 and the adjacent portion of thetube 28 corresponds to the diameter of the smaller, or bottom end 62 ofthe tapered center core 26 (FIG. 5).

A plurality of tubes are in fluid communication with the end of the tube28. Thus, the aperture port 30 is in fluid communication with the tube28 and extends radially outward from the tube 28 and the bottom cap 40.Oriented about 180° opposite to the port 30 is an arterial temperatureport 122. Located at about 90° to the port 30, is an arterialrecirculation port 124, which is in fluid communication with the centerof the tube 28.

Referring to FIGS. 3 and 5, the assembly of the oxygenator 12 will nowbe described. Two subassemblies are separately assembled as previouslydescribed, the enclosed fiber bundle unit 54, and the enclosed heatexchanger unit 56. The enclosed fiber bundle unit 54 is then insertedthrough the aperture 108 in the outer casing cap of the enclosed heatexchanger unit 56. The taper on the interior housing 20 and the interiorportion of coils 16 are substantially the same and oriented in the samedirection. Thus, the smaller end of the enclosed fiber bundle until 54can be readily inserted into the larger opening 108 in the enclosed heatexchanger unit 56.

The relative sizing of the components is such that the O-ring 77 on thesmaller, or bottom of the interior housing 20 abuts the interior side ofthe bottom portion 94 of the outer casing 92 when the enclosed fiberbundle unit 54 is resting on the inside of the enclosed heat exchangerunit 56. Similarly, the O-ring 79 on flange 78 abuts the inside of theflange 109 on outer casing cap 52. Further, the coils 16 abut theoutside diameter of interior housing 20. A force is then applied to theenclosed fiber bundle unit 54 to force the tapered parts into a tighterfit. Applying an 80-pound force by an air piston in contact with thelarger, or top end of the enclosed fiber bundle unit 54 has been foundsuitable.

The coils 16 limit the fit between the enclosed fiber bundle unit 54 andthe enclosed heat exchanger unit 56. After the parts are forced intothis tight fit position, the heat exchanger coils 16 are in asubstantially tight fit in the annular space defined between the wallsof the outer casing 92 and the walls of the interior housing 20 alongthe length of the middle portion 96. The flange 76 on interior housing20 (FIG. 4) helps limit the position of the enclosed fiber bundle unit54 with respect to the enclosed heat exchanger unit 56 as the flange 76would contact the coils 16 to limit relative motion between units 54 and56. The flange 76 also insures the coils 16 are not positioned so as toblock the apertures 78 which allow fluid flow into the enclosed fiberbundle 22.

The O-ring 77 provides a fluid-tight seal between the bottom of theinterior housing 20 and the bottom portion 94 of the outside casing 92.The L-shaped flange 78 at the larger end, or top of the enclosed fiberbundle unit 54 is resiliently urged against the flange 109 on the endcap 52 of the enclosed heat exchanger unit 56. The O-ring 79 on flange78 provides a seal between the top portions of the enclosed fiber bundleunit 54 and the enclosed heat exchanger unit 56.

To ensure that a gastight seal exists, beads of adhesive can be placedat appropriate points along any exposed and accessible interfacesbetween the enclosed fiber bundle unit 54 and the enclosed heatexchanger unit 56. Placing the adhesive adjacent the O-rings 77 and 79is believed suitable.

The top and bottom caps 32, 40, respectively, are then attached and, ifappropriate, sealed in place with an adhesive to ensure gastight joints.Specifically, the one-way valve 69 is connected to the port 118 in thetop cap 32. The flange 114 on top cap 32 is then inserted into theaperature 108 on the outer casing cap 52. The bayonet tabs 116correspond with the bayonet alots 113 to allow the insertion. After itis inserted, the cap 32 is rotated to lock the bayonet tabs 116 intoposition and prevent inadvertent removal of the top cap 32. Adhesive maybe placed in the groove between flange 78 and the top portion ofinterior housing 20 to seal with the lip 114 on top cap 32. The top cap32 defines a gas tight enclosure or gas manifold communicating with thetop 36 of the fiber bundle 22.

The bottom cap 40 is inserted such that the O-rings 120 on tube 28 sealagainst the cylindrical portion on the inside of the center core 58. Abead of adhesive is advantageously placed between the O-rings 120 toinsure a seal. The projections 119 fit in the slots 97 in the lower lip95 of the outer casing 92. After insertion, a rotation of the bottom cap40 positions the tabs 119 so they no longer coincide with the slots 97and thereby inhibits inadvertent removal of the bottom cap 40.

The bottom cap 40 provides a gas enclosure or gas manifold communicatingwith the gas outlet end of the fiber bundle 22, namely the bottom end38. For safety reasons, the bottom cap 40 is not completely sealed tothe outer casing 92. Outlet port 42 channels gas away from this gasmanifold.

The use of separate subassemblies for the heat exchanger unit and theblood oxygenator unit provides much simpler and quicker manufacturingand assembly than has previously been available. The use of the taperedfit on the major subassemblies allows the use of larger tolerances inmanufacturing and accommodates errors in assembly which leads to aquicker and faster assembly while providing a good seal on the unit.

The illustrated design facilitates testing for leakage. The flow path ofthe heat exchanger fluid may be tested at the subassembly stage when thecoils 16 are sealed in place to the casing 92, but more advantageously,after the outer casing cap 52 is glued in position and all of thepotting material 102 is inserted and cured. If a leak is detected atthis subassembly stage, appropriate steps may be taken without risk ofdamaging, or discarding the remainder of the oxygenator 12.

The use of two caps, the top cap 32 and outer casing cap 52, also allowsaccess to the end 36 of the fiber bundle unit 22 to greatly facilitatetesting of the fluid flow path and the gas flow path. Before the top cap32 is sealed in place, water may be pumped through the oxygenator 12 todetect leaks. Specifically, water may flow, under operating pressure,across the heat exchange coils 16, through apertures 18, through theenclosed fiber bundle 22, and out apertures 24 in center core 58. Ifthere is a leak in the fluid flow path, it may be detected andappropriate remedial steps, if any, taken. The pressurized water willalso enter through any leak in the fiber bundle, and flow through thefiber tube until water appears on the ends 36, 38 of the fiber bundle22. Thus, one test checks both the entire fluid flow path and the gasflow path through the fiber bundle 22.

The placement of the O-ring seals 77 and 79 (FIG. 4) between theenclosed fiber bundle assembly 54 and the enclosed heat exchangerassembly 56 also insures that a leak across the seals does notcontaminate the oxygenating gas flow path. Any leak of fluid into theinside of the fibers in the fiber bundle 22 will degrade the oxygenationperformance of the oxygenator 22. A leak across seal 79 may allow fluidto leak to the outside of the oxygenator 12, but the sealed lip 114 ontop cap 32 prevents any fluid from entering the gas flow path into theinside of the fibers. A leak across seal 77 is into the post oxygenationportion of the gas flow path, in to an unsealed chamber so any fluidwill not travel upstream against the flow of the gas into the fiberbundle. Thus, the seal design between the sub-assembled units 54 and 56insures against fluid leakage into the oxygenating gas flow path.

The use of the resiliently mounted O-ring 77 on the larger end of theenclosed fiber bundle unit 54, allows the more rigidly mounted seal 77to be seated by axially positioning the unit 54, while the resilientmounting of seal 78 accommodates that axial motion. Both seals 77 and 78accommodate axial motion of the enclosed fiber bundle assembly 54. Theresilient mounting of seal 77 thus allows for easier assembly of theunit, and allows a wider variability in manufacturing tolerances to beused.

The concentric arrangement of the heat exchanger coils 16 with the fiberbundle 22 allows a folding of the fluid flow path before oxygenationwhich in turn provides a location for placing a bubble trap to collectand remove bubbles from the fluid. The flange 76 is placed so as todirect the flow of fluid into the bottom of the bubble trap formed bythe space between flanges 109, 111 on the outer casing cap 52 (FIG. 4).

The tube 68 communicates oxygenated blood from the bottom of the fiberbundle 22, through the inside of the oxygenator, to a port 118 which iseasily accessible at the top of the oxygenator. The location of thearterial sample port 118 on the top of the oxygenator 12 provides areadily accessible means for the purfusionist to sample the oxygenatedblood, without having to bend outwardly and grapple with the bottom ofthe unit. Moreover, the internal routing of the tube 68 preventsinadvertent damage to or pulling of the tube 68.

The space between the flanges 109, 111 on the inside of the top cap 32is in fluid communication with the annular space containing the heatingcoils 16. Since the space between the flanges 109, 111 is positionedabove the coils 16, and positioned above the apertures 18 through whichthe blood flows into the fiber bundle 22, the space between the flangesacts as a gas trap to capture any gas bubbles dissolving out of theblood flowing through the oxygenator 12. The venous port 112 is in fluidcommunication with this space between the flanges 109, 111, and it canbe used to remove not only any excess gas, but to sample the blood atthis point in the oxygenator 12.

The use of a concentrically positioned heat exchanger and bloodoxygenator also allows a much smaller and more compact unit thanpreviously available. The use of the concentric heating coil and bloodoxygenator also provides some increase in the efficiency of the heatexchange unit in the sense that only the interior housing 20 separatesthe blood flowing around the fiber bundle 22 from the heat exchangecoils 16. Thus additional heat transfer from the coils 16 can occurthrough the interior housing 20 to the blood in fiber bundle 22 in orderto provide an increased efficiency of the heat exchanger.

The described arrangement of the heat exchanger coils 16 in conjunctionwith the concentric blood fiber bundle 22 also results in a low pressuredrop in the blood oxygenator 12. Thus, an 11 psi static flow pump isbelieved suitable for use.

An oxygenator 12 suitable for use with an adult has an approximatesurface area of the fibers 70 and the fiber bundle 22 of about 2 squaremeters. The priming volume is approximately 400 milliliters. The bloodflow rate through such a unit can be varied between one and seven litersper minute, with a maximum gas flow rate of 15 liters per minute. Themaximum water pressure through the heat exchange coils 16 isapproximately 80 pounds per square inch for a one-half inch diameterinlet and outlet ports 44, 50, respectively. The various casing and capcomponents of the oxygenator can be made out of a clear polymer materialsuch as polycarbonate, acrylic, ABS, SAN, etc.

The 2° taper described in the illustrated embodiment is believedsuitable for use. While a slightly smaller taper may be suitable foruse, the amount of taper should be greater than that normally used toensure easy release during molding of the critical plastic injected partfor blood oxygenators. For example, the mold release taper for acontainer in which a fiber bundle would be positioned is typically amaximum of 1/2° to 1°, with the goal being a zero degree taper. Priorpractice was to attempt to obtain no taper at all because any gapbetween the fiber bundle and the container allows blood to shunt orbypass the fiber bundle by flowing through that gap. Thus, the presentinvention goes against conventional practice by placing a taper on partswhich were previously designed and manufactured with the goal ofeliminating any taper whatsoever.

On the other hand, too great of a taper angle on the parts will limitthe amount of adjustability and tolerance variation which can beaccommodated when fitting the enclosed fiber bundle unit 54 into theenclosed heat exchanger unit 56. As the taper angle increases, lessaxial motion of the respective parts is required in order to create thesame amount of interference fit between the parts. Thus, while greatertapers may be possible, a taper angle of about 2°-6° is believeddesirable, and 2°-4° is believed even more advantageous for the taper onsuch components as the interior housing 20, the fiber bundle 22, and theassembly of coaxial coils 16.

In a further embodiment of this invention shown in FIG. 11, an adapter130 is used to removably attach a venous reservoir 132. The adapter 130comprises a generally tubular cylindrical structure having an innerdiameter sized to fit over the outside diameter of the circular portionsof outer casing cap 52. There are a plurality of slots 134 in the bottomportion of the adapter 130 which are located to coincide with thelocation of any components which extend radially outward of the outerperiphery of the outer casing cap 52. Such projections would include thetabs 106 and the ports 34 and 118.

There is a flange 136 extending radially inward of the adapter 130 andlocated such that when the adapter 130 is positioned on the oxygenator12, the flange 130 abuts against a portion of the outer casing cap 52 inorder to position it and stabilize the adapter 130.

At the top end of the adapter 130 is a flange 138 which extends radiallyoutward from the center of the adapter 130. A screw thread 140 is formedin the top of the adapter 130 on the inside of the cylinder. The venousreservoir 132 (shown schematically) has a corresponding set of externalthreads (not shown) which allow the venous reservoir 132 to be removablyengaged with the adapter 130.

The adapter 130 allows the venous reservoir 132 to be removably attachedto the blood oxygenator 12. The venous reservoir 132 is used to holdsufficiently large volumes of blood to handle normal fluctuations inflow returning from the patient. The adapter 130 allows a single venousreservoir to be used before, during, and after surgery, without havingto replace the venous reservoir or disconnect and reconnect a pluralityof connecting tubes.

While certain features of this invention have been described in detailwith respect to various embodiments thereof, it will of course beapparent that other modifications can be made within the spirit andscope of this invention.

What is claimed is:
 1. A method of manufacturing a hollow fiberoxygenator, comprising:forming a heat exchanger unit, comprising thesteps of:forming a plurality of heat exchanger coils into a coaxialassembly tapered at a predetermined angle along a longitudinal axis;enclosing said coils in a casing to define a heat-exchanger unit portionof a fluid flow path around the exterior of the coils; providing fluidcommunication means for passage of a temperature controlled fluidthrough the inside of said coils; forming an enclosed fiber bundlehaving a plurality of hollow microporous fibers wound about a centralcore, an interior housing encircling said fiber bundle, the ends of saidfiber bundle being cut and sealed between adjacent fibers so gas canpass through the length of said hollow fibers but not around said fibersto the inside of said enclosed fiber bundle, apertures being formed insaid interior housing and said central core to define a fiber bundleunit portion of said fluid flow path through said interior housing tothe inside of said enclosed fiber bundle around the outside of saidfibers and into said core; positioning said enclosed fiber bundleconcentrically inside said coaxial assembly of coils so said interiorhousing completes said heat exchanger unit portion of said fluid flowpath and provides fluid communication between said heat exchanger unitportion and said fiber bundle unit portion of said fluid flow path,wherein heat transfer can occur through said interior housing; attachinggas communication means to the opposing ends of said enclosed fiberbundle to communicate with the inside of said hollow fibers.
 2. A methodas defined in claim 1, comprising the further step of:providing limitedfluid communication means between the ends of said central core; andproviding exterior fluid access means on said oxygenator communicatingwith said limited fluid communication means to allow sampling of fluidafter it passes through said apertures in said central core.
 3. A methodas defined in claim 2, comprising the further step of:shaping saidapertures in said central core so there is a larger openingcommunicating with the fiber bundle than communicates with the inside ofsaid central core.
 4. A method as defined in claim 1, including the stepof forming said housing with an exterior taper between about 2° and 6°.5. The method of claim 1, wherein said heat exchanger unit comprises aplurality of separate heat exchanger coils and wherein each of saidcoils has an inlet end and an outlet end, additionally comprising thesteps of:providing an inlet header for introducing a temperaturecontrolled fluid of substantially uniform temperature into the inletends of said coils; providing an exit header for removing saidtemperature controlled fluid from the outlet ends of said coils;
 6. Themethod of claim 1, wherein one end of said enclosed fiber bundlecomprises a gas outlet end, additionally comprising the step ofattaching said gas communication means in a non-sealing manner to saidgas outlet end.
 7. A method manufacturing a hollow fiber oxygenator,comprising:assembling a heat exchanger unit, comprising the stepsof:coaxially stacking a plurality of individual heat exchanger coilshaving an inlet end and an outlet end in a casing to contain said coils,said coils being assembled to define a center cavity within said coils;and providing an inlet header for introducing a temperature controlledfluid of substantially uniform temperature into the inlet ends of saidcoils; providing an exit header for removing said temperature controlledfluid from the outlet ends of said coils; assembling an enclosed fiberbundle, comprising the steps of:forming a tubular central core with aplurality of apertures through the walls of said core adjacent a firstend, and a plug between said apertures and a second end of said core;winding a plurality of hollow microporous fibers about said core to forma bundle of fibers, the fibers extending the length of said bundle froma first end to a second end which correspond to the first end of saidcore and a second end of said core, respectively; sealing the ends ofsaid fibers adjacent the first and second ends of the core sufficientlyto prevent passage of gas between said fibers; forming an interiorhousing slightly smaller than the corresponding outside dimensions ofthe fiber bundle; forming a plurality of housing apertures in a secondend of said housing adjacent the second end of the central core whenassembled; placing the housing over said fiber bundle to encase it,thereby defining a fluid passage between said housing and said core andaround the fibers of said fiber bundle, the ends of said housing beingsealed to said fiber bundle; cutting through the sealed portion of saidfibers at said first and second ends to create open ends for said hollowfibers; inserting said enclosed fiber bundle into the center cavity insaid coils to define an annular fluid passage containing said heatexchanger coils, said annular passage communicating with said housingapertures; sealing the first and second ends of said housing to thefirst and second ends of the outer casing, respectively; and attachinggas communication means to the first and second ends of the fiberbundle.
 8. A method of manufacturing as defined in claim 7, furthercomprising the step of:providing limited fluid communication meansbetween the ends of said central core; and providing exterior fluidaccess means on said oxygenator communicating with said limited fluidcommunication means to allow sampling of fluid after it passes throughsaid apertures in said central core.
 9. The method of claim 7,additionally comprising the step of attaching said gas communicationmeans to said first end of said fiber bundle in a non-sealing manner.